COOKE: GEOGRAPHICAL DISTRIBUTION OF MOLLUSCA. 137 



species, while the Vivipara is regarded by some as a mere variety of 

 V. bengalensis Lam. The Isidora is of a distinctly African type, and 

 may have been introduced. The Lantzia, which is entirely peculiar 

 to Bourbon, is probably* closely allied to the very remarkable 

 Catnptonyx, which is exclusively Indian. It lives t in wet moss at 

 an altitude of upwards of 3,600 ft. Two of the Melanioz {scabra 

 Mull, amarula Lam.) are of an Indian type, which does not occur 

 in Africa. The Paludomus, although specifically identical with the 

 single African species (which significantly occurs in the Somali 

 district), belongs to a genus otherwise confined to India, Ceylon, 

 Further India, and Sumatra. Owing no doubt to the paucity of 

 permanent streams, no fresh-water bivalves occur. Among the 

 Neritidic is a single Septaria, which is common to the whole group, 

 except Rodriguez. This genus again, though occurring in Madagascar, 

 is entirely strange to the African continent, and is abundantly repre- 

 sented in the Palaeotropical and Australasian regions. 



It appears then, on the whole, that the Mascarenes proper are, 

 as we should expect, very closely connected, while the Seychelles 

 stand considerably apart, with a fauna of markedly Indian affinities. 

 Thus Pachystyla, Gibbus and Omphalotropis, the prominent 

 features of the Mascarene fauna, are entirely absent from the 

 Seychelles, while Cyclostoma is represented by only one species. On 

 the other hand, 4 sp. Pachnodus and 1 Streptaxis indicate an 

 African element in the Seychelles fauna, while the development of 

 the remarkable genus of Helix, Stylodonta, relates them to the great 

 Helices of Madagascar. At the same time their Indian and 

 Polynesian affinities are abundantly attested by the Cyathopoma, 

 Leptopoma, Helicina, Patula, and Paludomus. It would seem 

 probable that when the closer connection which at one time 

 undoubtedly existed between India and Eastern Africa began to be 

 less continuous,^ the Mascarene group was first severed from what 

 ultimately became Madagascar, while the Seychelles, and perhaps 

 the Comoros, still continued united to it. The Comoros, which lack 

 the great Helices, separated off from Madagascar first, while the 

 Seychelles continued in more or less direct union with that island 

 sufficiently long to receive the progenitors of Stylodonta, but became 

 disunited at an exceedingly remote period. 



G. Nevill, Handlist I. p. 215. 



t Jousseaume, ReV. Mag. Zool. 2 S. xxiii. pp. 5-9. 



t It is by no means implied that unbroken land communication between India and 

 Madagascar, across the Indian Ocean, ever existed. A series of great islands, whose remains 

 are attested by the Chagos and other banks, would be quite sufficient to account for the results, 

 as we find them. See especially Medlicott and Blanford, Geology oj India, vol. i. p. Ixviii. 



